Internal combustion engine manufacturers are constantly seeking to increase power output and fuel efficiency of their products. One method of generally increasing efficiency and power is to reduce the oscillating mass of an engine, e.g., of the pistons, connecting rods, and other moving parts of the engine. Efforts to increase engine power and/or efficiency may also result in an increase in pressure and/or temperature within the combustion chamber during operation.
Engines, and in particular the pistons of the engine, are therefore under increased stress as a result of these reductions in weight and increased pressures and temperatures associated with engine operation. Piston cooling is therefore increasingly important for withstanding the increased stress of such operational conditions over the life of the engine.
To reduce the operating temperatures of piston components, an internal cooling gallery may be provided about a perimeter of the piston. A coolant such as crankcase oil may be introduced to the cooling gallery during piston operation, and may be distributed about the cooling gallery by the reciprocating motion of the piston, thereby reducing the operating temperature of the piston.
The cooling galleries may increase overall complexity of the piston and manufacturing of the same. For example, cooling galleries may include an additional component, such as a cooling gallery cover, in order to encourage and direct proper circulation of a coolant throughout the cooling gallery by temporarily trapping coolant (e.g., oil) that is circulated through the cooling gallery. The additional components (such as cover plates) also add complexity, however, and may be expensive and/or difficult to form in smaller piston applications such as in the case of lightweight or light duty pistons. Additionally, known methods of forming enclosed cooling galleries in one-piece pistons, such as friction welding, include extremely high strength piston components to properly form the piston and cooling gallery features without unintended deformation during the friction welding process, thereby increasing size and weight of the resulting pistons. The large magnitude forces placed on the piston components during the friction welding process also limits where the weld joints may be located.
As such, other known methods of forming enclosed cooling galleries in one-piece pistons include laser welding of the cooling gallery cover to the piston. Typically the piston is initially formed having the cooling gallery formed therein, a cooling gallery ring is separately formed, and the cooling gallery cover is laser welded to the piston in order to form the cooling gallery within the piston. In order to obtain complete penetration of the weld, sufficient power is provided such that a fusion joint is formed throughout the depth of the parts being welded. However, in so doing a weld spatter is caused to emit from the weld or fusion joint, causing particulate to adhere to inner portions of the cooling gallery. The weld spatter can be difficult to remove because the spatter can attach to the walls of the cooling gallery and once the cooling gallery ring is attached. If weld spatter cannot be removed from within the cooling gallery, production parts may have to be scrapped because spatter can interfere with coolant flow or could cause performance issues with the piston if the spatter were to break free during operation.
Accordingly, there is a need for a laser welding process in formation of a cooling gallery in which weld spatter into the cooling gallery is minimized.